I have a problem with regulating emotions so I pretty much live on an emotional roller coaster all the time haha. The best thing to do when you're feeling a low or negative is to allow yourself to feel the emotion, sit with it but then do a meditation to get it out, but don't bury it exactly or it just festers inside of you and doesn't get released. Whenever I'm sad I let myself cry and then if I can, take a nap, or if I'm out, go and sit in nature for a little while or somewhere quiet and calm, or if I'm stuck in class, I just tell myself that I'll allow myself to feel the emotion soon, just get through this class first, hope that helps